The MPR web site http://mpr.nci.nih.gov contains information about human phosphorylation sites against which there are commercially available phospho-antibodies. Major progress has been made in MPR in FY 2004. At the outset of FY2004, MPR consisted of a single static web page of high quality information. Development during 2004 has involved adding content, changing to a coherent data-driven collection of dynamic web pages, adding additional unique functionality to the site, and facilitating access via search engines such as Google by altering details of web page structure and meta-information. The result has been a striking growth of utilization. The user can gain access to the information in MPR in several ways: by browsing a list of all proteins for which phospho-antibodies are available; by searching for sites on an individual protein, or by browsing lists of phospho-antibodies from any particular company. Information provided for a site includes the exact sequence of surrounding residues (which is critical to unambiguous identification of the site of interest), a list of antibodies available against that site, several critical parameters for those antibodies, direct links to the supplier's web site information on each antibody; and links to pubmed citations related to that site. MPR also provides links to other web pages for each gene/protein that facilitates user exploration of resources including Genbank, Locuslink, CGAP, and Symatlas pertinent to their studies. Additional functionality provided is the ability to search for a site (and antibodies) based on the sequence of that site. Not only does that allow rapid/easy retrieval of the site information on that site, it also allows the user to survey sites of similar sequence that may be observed as cross-reactions or may have functional similarities. In addition, MPR now provides a curated collection of links that directs users to other particularly informative web cites relevant to protein phosphorylation. We have developed a novel, more accurate approach to determining detailed peptide specificity for several PKC isoforms and to predict sites in proteins most likely to be phosphorylated by PKC. We have added to MPR a component that allows users to submit the sequence of their protein of interest, and provides them a graphical output that summarizes information on predicted sites of phosphorylation. In additional the users can elect to download a Excel spreadsheet of this information to facilitate their further analysis of phosphorylation of this protein. It should be also noted that the infrastructure we have developed for MPR has facilitated our role in organizing information on phosphorylation sites for the CCR/BD collaboration.